RosettaCodeData/Task/Substring/BQN/substring.bqn

   5↑3↓"Marshmallow"
"shmal"
   3↓"Marshmallow"
"shmallow"
   ¯1↓"Marshmallow"
"Marshmallo"
   (⊑∘/'m'⊸=)⊸↓"Marshmallow"
"mallow"
   (⊑∘/"sh"⊸⍷)⊸↓"Marshmallow"
"shmallow"